Specialist Thomas McArdle (left) works with traders at the post that handles Dow Chemical on the floor of the New York Stock Exchange. If a proposed merger goes through, Dow's and DuPont's respective shareholders would own about half of the new entity. Richard Drew/AP hide caption

toggle caption Richard Drew/AP

Soybeans are sprayed in Iowa in 2013. Enlist Duo is a mixture of two chemicals that farmers have used separately for many years: glyphosate (also known as Roundup) and 2,4-D. The new formulation is intended to work hand-in-hand with a new generation of corn and soybean seeds that are genetically engineered to tolerate sprays of both herbicides. Charlie Neibergall/AP hide caption

toggle caption Charlie Neibergall/AP